_First_, when anything touches the cells without harming them, we feel a _touch_. We feel a touch by nerves in the skin. Those in the ends of the fingers and tongue can feel the best. Those upon the back give but little feeling. Touch tells whether anything is hard, or rough, or round, or square, or has other qualities and shapes. _Second_, when anything touches the bare nerves or hurts the cells, we feel a _pain_. We can feel a pain anywhere in the body. Pain tells us if we are being harmed. If we had no feeling of pain, we might be killed before we could know of our danger. Pain warns us away from danger. _Third_, we can feel _heat_ and _cold_. Anything very hot or very cold, however, makes only a pain and gives no feeling either of cold or of heat. =164. Sight.=--We see with our eyes. An eye is a hollow ball. In its front is a clear window. Behind the window is a round curtain with a round hole in its middle. When we speak of the color of the eye, we mean the color of this curtain. Light passes through the hole in the curtain and falls upon some nerves in the back of the eyeballs. There it forms a picture like a photograph. The nerves carry this picture to the brain, and we see it. [Illustration: =The human eye.= _a_ bony case of the eye. _b_ muscle to move the eye. _c_ and _d_ coverings of the eye. _e_ lining or seeing part of the eye. _f_ eyelid. _g_ colored curtain or iris. _h_ and _i_ clear windows of the eye.] =165. Movements of the eyes.=--We can turn our eyes so as to look in any direction. Sometimes a person has one eye turned sidewise. Such a person is cross-eyed, and sees well out of only one eye at a time. Glasses may help the eyes, but sometimes a surgeon has to cut a tiny muscle. =166. Coverings of the eyes.=--The eyeballs lie in a bony case, upon a soft bed of fat. In front each is covered with two lids. We can shut the lids to keep out dust and insects. When we are sleepy, they come together and cover the eyes. Little hairs at their edges help to keep out the dust. Sometimes a little dirt gets under the lids. Then the eye smarts or itches, and we want to rub it; but this may grind the dirt in deeper. Then you should get some one else to lift your eyelid and pick out the dust with a soft handkerchief. If you cannot get help, lift the lid by the eyelashes; blow your nose hard, and the tears may wash the dirt away. Dust and disease germs may get into our eyes and make them sore and red. You should bathe your eyes well every time you wash your face. You should use a clean towel, for a dirty one may carry disease germs to your eyes. Some forms of sore eyes are catching. If any one has sore eyes, no one else should use his towels or handkerchiefs. =167. Tears.=--Clear salt water is always running over the eyes and down a tube into the nose. The use of this water is to bathe the eyes and keep them clean. It sometimes runs over the lids in drops called _tears_.